**Question:** The muscles acting upon the temporomandibular joint for various actions are given below, EXCEPT:

A. Masseter muscle
B. Temporalis muscle
C. Stapedius muscle
D. Digastric muscle

**Core Concept:**
Temporomandibular joint (TMJ) is a synovial joint that connects the mandible (lower jaw) to the temporal bone of the skull. TMJ allows for various jaw movements such as opening, closing, and lateral and vertical movements of the mandible. The muscles surrounding the TMJ play a crucial role in these movements.

**Why the Correct Answer is Right:**
The correct answer, **C. Stapedius muscle**, is not part of the TMJ muscles because it is a muscle of the inner ear, specifically involved in hearing and balance functions. The other options (A, B, and D) are part of the masticatory muscles that surround and act upon the TMJ for various jaw movements.

**Why Each Wrong Option is Incorrect:**
A. **Masseter muscle** is a key masticatory muscle that acts upon the TMJ for opening and rests the mandible in the fossa for mastication (chewing).
B. **Temporalis muscle** is another masticatory muscle that acts upon the TMJ for opening, closing, and lateral movements of the mandible.
D. **Digastric muscle** is another masticatory muscle that acts upon the TMJ for opening, closing, and lateral movements of the mandible, while also assisting in mandibular elevation.

**Clinical Pearl:**
Understanding the correct function of each muscle surrounding the TMJ is essential for understanding jaw movements and their effects on the TMJ. Misidentifying a muscle like the Stapedius muscle as a masticatory muscle can lead to confusion regarding the anatomy and function of the TMJ and its associated muscles.

**Correct Answer:** C. Stapedius muscle